Generally, to form semiconductor devices such as transistors and capacitors on a semiconductor substrate, a device isolation layer is formed on a semiconductor substrate. The device isolation layer divides the semiconductor substrate into an active region that allows electrical conduction and a device isolation region that prevents electrical conduction and separates semiconductor devices from each other.
As recent semiconductor technology requires a fine device isolation technology in order to achieve high integration and low power consumption of devices, STI is widely used.
An STI process includes forming a trench having a predetermined height in a semiconductor substrate, depositing an oxide layer in the trench, and etching an unnecessary portion of the oxide layer to form a device isolation layer on the semiconductor substrate.
However, since an upper corner of an STI formed by the prior art is sharp, stress is concentrated on the upper corner during a subsequent thermal process, and thus a silicon defect is generated around the upper corner and an electric field concentration phenomenon during an operation of a device occurs.
Also, according to the prior art, when a field effect is concentrated on a corner of the trench of the device isolation layer, the leakage current of a semiconductor device increases.